Development of Compressed Air Insulation Technology for C-GIS

We have developed cubicle-type gas-insulated switchgears (C-GISs) applying compressed air insulation technology. To apply the compressed-air insulation to the C-GISs, we identify whether breakdown in compressed air depends on the maximum field strength on high-voltage conductors, and specify the relationship between the breakdown field strength vs. non-uniformity of the electric field distribution of gaps. In this work we use three types of sample gaps to simulate the inside structure of an actual C-GIS. Field utilization factor, U is used to express the non-uniformity of electric field distribution of the sample gaps. As a result, for all types of sample gap, the breakdown field strength at the point where the maximum field is generated on the high-voltage electrode increases as U decreases. There is only small difference in the breakdown field strength among sample gaps that have the same value of U. From these results, we judge that insulation design based on both the field strength on high-voltage conductor and U is possible. Furthermore, we provide an example of actual insulation design applied to a developed C-GIS.